Drug delivery devices allowing for multiple dosing of a required dosage of a liquid medicament, such as liquid drugs, and further providing administration of the liquid to a patient, are as such well-known in the art. Generally, such devices have substantially the same purpose as that of an ordinary syringe.
Drug delivery devices of this kind have to meet a number of user specific requirements. For instance in case of those with diabetes, many users will be physically infirm and may also have impaired vision. Therefore, these devices need to be robust in construction, yet easy to use, both in terms of the manipulation of the parts and understanding by a user of its operation. Further, the dose setting must be easy and unambiguous and where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose.
In order to meet these requirements, the number of parts and steps required to assemble the device and an overall number of material types the device is made from have to be kept to a minimum.
Typically, the medicament to be administered is provided in a cartridge that has a moveable piston or bung mechanically interacting with a piston rod of a drive mechanism of the drug delivery device. By applying thrust to the piston in distal direction, a certain amount of the medicinal fluid is expelled from the cartridge.
Drug delivery devices, such like pen-type injectors typically comprise a housing having a cartridge holder for receiving the cartridge filled with the medicament that has to be dispensed. The distal end section of a cartridge holder facing towards the patient during an injector procedure typically comprises a through opening that provides access to a sealed distal end of the cartridge. By way of said through opening, an injection needle or cannula may penetrate the elastic seal to establish a fluid interconnect allowing the medicament to be expelled from the cartridge.
Typically, the disposable injection needle is provided by way of a needle assembly for releasably fastening the injection needle to the cartridge holder. For this purpose, needle assembly and distal end section of the cartridge holder comprise mutually corresponding threads, by way of which the needle assembly is screwed onto the cartridge holder. However, a threaded connection of cartridge holder and needle mount comes along with a number of deficiencies. Such threaded engagement for instance, does not give a perceptible feedback to the user whether needle assembly is securely mounted on the cartridge holder. In practical use, situations may occur, that only a single or a few threads of a cartridge holder and a needle assembly inter-engage, but the needle assembly is not yet securely fastened to the cartridge holder.
A user may then simply not be not aware of such improper and insufficient fastening and may therefore initiate a dose selecting and dispensing procedure. In particular in the course of a dispensing of a dose of the medicament, the needle assembly may autonomously disengage from the cartridge holder, for instance due to a built-up of a fluid pressure and/or when penetrating the skin of the patient. In these cases, the patient would be exposed to an increased health risk.